High melt strength composition comprising modified polycaprolactam and impact modifier

ABSTRACT

Compositions are described, which are blow-moldable into shaped articles, comprising a reaction product between polycaprolactam, aminoalkyltrialkoxysilane and a catalytic amount of water. The compositions have a melt index of about 2.25 g/10 min. or below and are substantially free of trialkoxysilane groups. Preferred compositions also contain ethylene/vinyl acetate copolymer as an impact modifier to increase the impact strength of blow-molded articles made therefrom, such as bottles.

This is a division, of application Ser. No. 128,438, filed Mar. 10,1980, now U.S. Pat. No. 4,319,007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to high melt strength, high impact resistantpolycaprolactam compositions, containing aminoalkyltrialkoxysilanecompound, a process for producing same and products made therefrom.

2. Brief Description of the Prior Art

Although polyamide molding compositions and other polymers having lowmelt strength values have met with a high degree of commercial success,they are generally not used for applications where a particular meltstrength is required, such as in blow-molding processes to producebottles or other relatively heavy duty containers.

U.S. Pat. No. 3,673,155 (June 27, 1972) describesbis(aminoorganosilyl)hydrocarbon-modified polyamides useful as moldingcompounds and insulating film. However, the reference does not describecompositions, useful in blow molding applications, which have high meltstrength.

U.S. Pat. No. 3,341,501 (Sept. 12, 1967) describes linear polyamidecompositions having organosilane end groups, which can be bonded toglass or metal with a tenacity that withstands boiling water. However,the reference does not describe polyamide compositions having high meltstrength which are useful in blow-molding applications.

There is a need in the art to modify polyamide compositions,particularly polycaprolactam having a low melt strength value, in such away as to improve both its melt strength as well as its stability atelevated temperatures. Potential markets for blow-molded polycaprolactamhave not been effectively developed owing to the fact that the meltstrength of conventional polycaprolactam compositions is not high enoughfor practical blow-molding operations. In view of its low melt strength,conventional polycaprolactam compositions, even with close temperaturecontrol, form parisons lacking in integrity which have a tendency toneck-in. These parisons do not widen, whereas parisons prepared frommaterials having high melt strength, such as polyolefins, swell and dropeasily over the blow pin in a blow-mold operation.

Therefore, polycaprolactam compositions having high molecular weight,high tensile strength, and capable of being blow-molded into relativelylarge heavy duty containers, are not presently commercially available.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a polycaprolactamcomposition capable of being blow-molded into a shaped article.

Generally, the composition possesses a sufficient melt strength for theblow-molding of shaped articles and comprises the reaction productbetween polycaprolactam, aminoalkyltrialkoxysilane and a catalyticamount of water, said reaction product being substantially free oftrialkoxysilane groups and said composition possessing a melt index ofbelow about 2.25 g/10 min. Melt indexed is generally used as anindication of melt strength because melt strength is normally inverselyproportional to the melt index. Thus, as the melt index increases themelt strength can be expected to decrease in proportion thereto.

A preferred embodiment is where the composition contains a reactionproduct of polycaprolactam, ethylene/vinyl acetate copolymer,gamma-aminopropyltriethoxysilane and a catalytic amount of water and thecomposition possesses a melt index of about 1 to 2 gram/10 min.

A process for producing the subject composition is also provided andcomprises reacting polycaprolactam with an aminoalkyltrialkoxysilane, inthe presence of a catalytic amount of water, at a temperature of about225° to 350° C.

Further provided is a shaped article of manufacture produced byblow-molding the subject composition.

DETAILED DESCRIPTION OF THE INVENTION

The polycaprolactam to which the present invention applies includes thathaving a weight average molecular weight of at least about 10,000 andcontaining various amino and carboxyl types of terminal functionality.Preferred are the polycaprolactams (nylon 6) containing: (a) carboxylgroups attached to each end of the polymer chain; (b) a carboxyl groupattached to one end and an acetamido group attached to the other end ofthe polymer chain; (c) an amino group attached to each end of thepolymer chain; and (d) a carboxyl group attached to one end and an aminogroup attached to the other end of the polymer chain. More preferred isa polycaprolactam having a carboxyl group attached to one end and anamino group attached to the other end of the chain.

The polycaprolactam can be produced by any conventional process known inthe art. Illustrative of one such process involves two steps: the firststep consists of heating epsilon-caprolactam and hexamethylenediamineand water to a temperature of about 180° to 300° C. undersuperatmospheric pressure (about 200 to 280 lbs/in²) to effect partialpolymerization; the water is allowed to distill gradually from thereaction mixture while the polymerization continues after most of themonomer has been converted to a low molecular weight polymer; thepressure is reduced to atmospheric pressure wherein the second step iscommenced which comprises completing the polymerization by heating atatmospheric pressure at a temperature of about 180° to 300° C.

Polycaprolactam useful in the present invention has a melt index (ASTMD-1238) of about 3 to 12 or greater, and preferably of about 3 to 6grams/10 minutes.

It is important that the polycaprolactam whose melt strength is to bemodified contain a catalytic amount of water to initiate the reaction ofone aminoalkyltrialkoxysilane compound with another. Generally, theamount of water needed is about 0.05 to 5 weight percent based on thetotal weight of the polymer. By the term "catalytic amount" is meant theminimum amount needed, based on stoichiometry, to initiate thehydrolysis reaction of the aminoalkyltrialkoxysilane molecules therebyleading to a condensation and thus releasing additional water tomaintain the overall reaction process.

Included among aminoalkyltrialkoxysilane compounds, or "aminosilane"compounds as used herein, suitable for use in the present invention arethose compounds represented by the formula: ##STR1## wherein R', R" andR"' are independently monovalent C₁ to C₁₈ linear or branched alkyl oraryl or alkyl-aryl; or R is a divalent C₁ to C₁₈ linear or branchedalkylene alkylenaminoalkylene. The above-described groups can also besubstituted with one or more substituents inert under the processconditions for forming or using the subject compositions including C₁ toC₄ alkoxy or halogen, such as chloro, fluoro and trifluoromethyl groups.

Representative examples of such aminosilane compounds includegamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,beta-aminoethyltriethoxysilane, delta-aminobutyltriethoxysilane,gamma-aminopropyltripentoxysilane andN-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane. Preferred aregamma-aminopropyltrimethoxysilane and gamma-aminopropyltriethoxysilane.

The amount of aminosilane compound that is used is about 0.1 to 1.0weight percent of the composition, and preferably about 0.2 to 0.5weight percent. Larger amounts lead to great difficulty in processingthe composition, and smaller amounts lead to insufficient melt strengthsfor blow-molding applications.

The subject composition is a reaction product between polycaprolactamand an aminosilane compound. It is believed that the amino group in theaminosilane reacts with free carboxyl group in polycaprolactam providingtrialkoxysilane end-capped polymer and with the amide group in thepolycaprolactam chain thus decreasing the chain length size. In thepresence of the catalytic amount of water, the trialkoxysilane groupsare hydrolyzed to produce --Si(OH)₃, which then reacts with another--Si(OH)₃ group to produce --Si--O--Si--O-- linkages and thus bindtogether the two strands of polycaprolactam. It is believed that theincrease in melt strength is due to branching of the polycaprolactampolymer chains which occurs during the above-described hydrolysis andcondensation of trialkoxysilane groups. Due to the water initiallypresent, and that produced during the condensation reaction, it isbelieved that substantially all of the trialkoxy groups initiallypresent are reacted in the final subject composition.

The required melt strength of the subject composition, for operabilityin blow-molding processes, is achieved by the composition possessing amelt index of below about 2.25 g/10 min (ASTM D-1238). Preferred is amelt index of about 1 to 2 g/10 min.

The addition of the aforementioned aminosilane compounds to normally lowmelt strength polycaprolactam surprisingly increases the melt strengthof the composition and renders it capable of being blow-molded intorelatively heavy-duty containers and extruded into heavy-duty rods andtubes.

The impact resistance, although in some cases adequate, may be increasedto a value equivalent to a drop weight value (ASTM D-2444) of at least97 ft-lbs., by the use of an impact modifier such as ethylene/vinylacetate copolymer.

The impact resistance can be substantially increased by the addition ofabout 1 to 50 wt. %, preferably about 3 to 30 wt. %, and more preferablyabout 5 to 20 wt. %, based on the total weight of the composition, of acopolymer having functional groups attached thereto which are compatiblewith the polycaprolactam substrate. Representative examples of suchgroups include esters, ethers, acids, anhydrides, epoxides, halides,isocyanates, isothiocyanates and carboxyl groups. Preferably, thecopolymer is comprised of a diene or an olefin with one or morecomonomers containing any of the aforementioned functional groups. Morepreferred are copolymers of ethylene or butadiene wherein the comonomercan be a vinyl ester such as vinyl acetate, vinyl salicylate, vinylstearate and vinyl propionate and the like; acrylate esters such asmethyl acrylate, ethyl acrylate, benzyl acrylate, octyl acrylate, methylmethacrylate, and the like; vinyl ethers such as vinyl 2-chloroethylether and methoxy polyethylene oxymethacrylate, and the like; andcarboxylic acids such as acrylic, methacrylic, itaconic, fumaric,maleic, citraconic, α-methylene glutaric, aconitic, methylene-malonic,mesaconic acids and substituted acrylic acids such as β-hydroxymethyl-or α -halomethyl acrylic acids as well as acids such asmethacryloxypropionic acid, acryloxy- or methacryloxyisopropyl acidphthalate, acryloxy- or methacryloxyethyl or isopropyl acid oxalate,maleate, succinate, glutarate and the like. Most preferably, thecopolymer is a copolymer of ethylene and vinyl ester such as a copolymerof ethylene and vinyl acetate.

Ethylene/vinyl acetate copolymer suitable for use herein is thatcommercially available in a variety of formulations. That suitable foruse in the present invention has a vinyl acetate content ranging fromabout 5 to 42 wt. % based on the total weight of monomers. Preferred isa formulation having a vinyl acetate content of about 25 to 35 wt. %, amelt index of about 3 to 6, an inherent viscosity of about 0.93, and adensity of about 0.953.

A presently preferred composition is that possessing sufficient meltstrength for the blow-molding of shaped articles comprising the reactionproduct between polycaprolactam, ethylene/vinyl acetate copolymer,gamma-aminopropyltrialkoxysilane and a catalytic amount of water, saidreaction product being substantially free of trialkoxysilane groups,said composition possessing a melt index of below about 2.25 g/10 min.and said ethylene/vinyl acetate copolymer being present in about 5-20weight percent of the composition and said aminosilane compound beingpresent in about 0.01 to 1.0 weight percent of said composition.

Generally, a process for preparing the subject polycaprolactamcompositions comprises feeding, into an extruder, a polycaprolactamresin containing a small amount of water, about 0.01 to 1.0 wt. % of anaminosilane compound, and optionally an impact modifier. The extrudercan be any conventional extruder used for the extrusion of plasticmaterials and generally contains an electrically heated barrel, ametering-type screw and a screen and breaker plate. The temperature ofextrusion is about 225° C. to 350° C., preferably about 300° C. Whenrelatively volatile aminosilane compounds are used it is preferred thatthe extruder contain more than one heated zone, preferably four heatedzones. The first zone is maintained at a temperature low enough so thatthe aminosilane compound does not volatilize, but at a temperature highenough so that the polyamide resin begins to melt and the ingredientscommence to react. This temperature is preferably about 225° to 245° C.,more preferably about 230° to 240° C. Zone two is maintained at atemperature of about 250° to 290° C., preferably 250° to 260° C. Zonesthree and four are maintained at a temperature of about 290° to 315° C.,preferably about 290° to 300° C. Although the number of heating zones ofthe extruder is not critical, it is preferred, when a volatileaminosilane compound is used, that the temperature range of the extruderbe about 225° to 245° C. at the point where the ingredients areintroduced and about 290° to 315° C. at the point further down theextruder and up to the screen and breaker section of the extruder. It isunderstood that when a high molecular weight nonvolatile silane compoundis used, the temperature throughout the extruder can be from about 290°to 315° C.

By "volatile aminosilane compound" we mean those aminosilane compounds,as previously stated herein, which are volatile at a temperature greaterthan about 230° C.

It is not critical to the present invention that the ingredients be fedinto the extruder as a blend of distinct compounds. For example, thefeed of ingredients can be comprised of a polycaprolactam resin, anaminosilane compound and optionally an impact modifier. The feed canalso be comprised of a copolymer of polycaprolactam and impact modifiercopolymer and an aminosilane compound; or, it can be comprised of apremixed blend of a polycaprolactam resin with an aminosilane compoundwhich is further mixed with the impact modifier before feeding into theextruder. It is understood that mixtures of the various polymerssuitable for use herein can be fed into the extruder with mixtures ofthe various aminosilane compounds suitable for use herein as well as theoptional impact modifier ingredient.

The subject compositions, after extrusion and forming, generally havethe following physical properties in the stated ranges: a tensileelongation-to-break of about 120 to 300% (ASTM D-638); a tensilestrength of about 10,000 to 15,000 psi (ASTM D-638); a flexural strengthof 13,000 to 15,000 psi (ASTM D-790); a flexural modulus of 350,000 to375,000 psi (ASTM D-790); a notched Izod impact of 2.0 to 2.5 ft. lbs.per inch of notch (ASTM D-256); a drop weight impact of 90 to 140 ft.lbs. (ASTM D-2444); and a melt index of about 0.1 to 2.25 g/10 min asmeasured by ASTM D-1238.

Also provided is a shaped article of manufacture, for example a 4 oz.bottle for non-food application, produced by blow-molding the subjectcomposition described herein.

The following examples are illustrative of the best mode contemplated byme of carrying out the invention and should not be considered as beinglimits on the scope or spirit of the instant invention.

EXAMPLE 1

11 Kg of a polyepsiloncaprolactam, having a Melt Index (M.I.) of 4.98g/10 min. and a water content of about 0.1%, and 55 g ofgamma-aminopropyltriethoxy silane, were introduced into an unvented twinscrew extruder having a four temperature profile of about 240°, 260°,250° and 245° C. The extruded material had an M.I. of 1.9 g/10 min. Thisexample shows the increase in melt viscosity of polyepsiloncaprolactamwhen reacted with an aminosilane.

EXAMPLES 2-7

9.25 Kg of polyepsiloncaprolactam having an M.I. of about 4.90 g/10min., and a water content of 0.1%, 750 g of ethylene/vinyl acetatecopolymer and various amounts of gamma-aminopropyltriethoxysilane wereintroduced into an unvented twin screw extruder having a temperatureprofile of about 230°, 300°, 300°, 300° and 260° C. at the die. The meltindex of the extruded materials were measured and the results are setforth in Table I below.

                  TABLE I                                                         ______________________________________                                                                 Silane                                                         Nylon EVA      Compound  M.I.                                                 Kg    Kg       g         g/10 mi                                    ______________________________________                                        Example                                                                       2           9.25    0.75     35.0    2.23                                     3           9.25    0.75     37.5    1.99                                     4           9.25    0.75     40.0    1.82                                     5           9.25    0.75     42.4    1.14                                     6           9.25    0.75     45.0    1.03                                     7           9.25    0.75     47.5    0.7                                      (Comparative)                                                                 (Comparative) A                                                                           9.0     1.0      0       5.5                                      (Comparative) B                                                                           9.25    0.75     22.5    2.85                                     (Comparative) C                                                                           9.25    0.75     25.0    2.62                                     (Comparative) D                                                                           9.25    0.75     27.5    2.60                                     (Comparative) E                                                                           9.25    0.75     30.0    2.44                                     (Comparative) F                                                                           9.25    0.75     32.5    2.31                                     ______________________________________                                    

The above table shows the melt strength of polyepsiloncaprolactam whenreacted during extrusion with increasing amounts ofgamma-aminopropyltriethoxysilane in the presence of ethylene/vinylacetate copolymer as an impact modifier. Examples 2-7 possessedsufficient melt strength to be blow-molded into bottles of 4 oz.capacity. The Comparative Examples A-F did not possess sufficient meltstrength to be blow-molded into 4 oz. bottles.

EXAMPLE 8

Bottles were melt blown with two different polyepsiloncaprolactammaterials. One material (Comparative Example G) was prepared by feeding,into an unvented twin screw extruder, 9.95 Kg of polyepsiloncaprolactamhaving a melt index of about 3.7 g/10 min. and 50 g ofaminopropyltriethoxysilane. The melt index of the resulting compositionwas 0.2. The other material (Example 8) was prepared by feeding, into anunvented twin screw extruder, 8.95 Kg of a polyepsiloncaprolactam havinga melt index of about 3.7 g/10 min., 1 Kg of EVA and 50 g ofgamma-aminopropyltriethoxysilane. The melt index of the resultingcomposition was 0.6. Both polycaprolactams contained about 0.1% water.The physical properties of the bottles are shown in Table II below:

                  TABLE II                                                        ______________________________________                                                     Comp. Example G                                                                           Example 8                                            ______________________________________                                        Wall thickness, mil                                                                          100           92                                               Weight of bottle, g                                                                           72           52                                               Drop. Wt. Impact                                                                             shatter       97                                               ft.lb/100 Mil                                                                 (ASTM D-2444)                                                                 ______________________________________                                    

The physical properties of the material of Example 8 are as follows:tensile strength, 10,840 psi (ASTM D-638); tensile elongation-to-break,130% (ASTM D-638); flexural strength, 13,900 psi (ASTM D-790); flexuralmodulus, 369,000 psi (ASTM D-256); drop weight impact, 97 ft. lbs. (ASTMD-2444).

These examples illustrate that an aminosilane compound, such asgamma-aminopropyltriethoxysilane, when incorporated intopolyepsiloncaprolactam, is surprisingly able to modify the polymersufficiently to achieve the melt strength required for melt blowing.Where there is a need for higher impact strengths, an impact modifiersuch as ethylene/vinyl acetate copolymer can be used to increase theimpact strength of the bottle for heavy duty practical use.

COMPARATIVE EXAMPLE H

10 Kg of polyepsiloncaprolactam having an M.I. of about 4.9 g/10 min.and a water content of about 0.1% was melt blended in an unvented twinscrew extruder having a temperature profile of about 500°, 500°, 550°and 600° F., with 55 g of octyltriethoxysilane. The resulting materialwas found to have an M.I. of 6.5 g/10 min. This example demonstratesthat not all organosilane compounds are suitable for use in improvingthe melt strength of polycaprolactam.

It is to be understood that variations and modifications of the presentinvention may be made without departing from the scope of the invention.It is also to be understood that the scope of the invention is not to beinterpreted as limited to the specific embodiment disclosed herein, butonly in accordance with the appended claims when read in light of theforegoing disclosure.

What is claimed is:
 1. A composition possessing sufficient melt strengthfor the blow-molding of shaped articles comprising the reaction productbetween polycaprolactam, having a melt index of at least 3 grams/10minutes, aminoalkyltrialkoxysilane, and a catalytic amount of water,said reaction product being substantially free of trialkoxysilanegroups, and said composition further comprising 1 to 50 percent byweight of the composition of an impact modifier, said compositionpossessing a melt index below about 2.25 g/10 min.
 2. The composition ofclaim 1 wherein said impact modifier is ethylene/vinyl acetatecopolymer.
 3. The composition of claim 1 wherein saidaminoalkyltrialkoxysilane is of the formula: ##STR2## wherein R', R" andR"' are independently monovalent C₁ to C₁₈ linear or branched alkyl; Ris a divalent C₁ to C₁₈ linear or branched alkylene oralkylenaminoalkylene.
 4. The composition of claim 3 wherein saidaminoalkyltrialkoxysilane is selected from the group consisting ofgamma-aminopropyltrimethoxysilane and gamma-aminopropyltriethoxysilane.5. The composition of claim 1 wherein said aminoalkyltrialkoxysilane ispresent in about 0.01 to 1.0 weight percent of the composition.
 6. Thecomposition as recited in claim 1 wherein the polycaprolactam has a meltindex of from 3 to 12 grams/10 minutes.
 7. The composition as recited inclaim 1 wherein the amount of the impact modifier is about 3 to 30percent by weight of the composition.
 8. The composition as recited inclaim 1 wherein the amount of the impact modifier is about 5 to 20percent by weight of the composition.
 9. A process for producing thecomposition of claim 1 comprising reacting polycaprolactam with anaminoalkyltrialkoxysilane in the presence of a catalytic amount ofwater, and the impact modifier at a temperature of about 225° to 350° C.10. The process of claim 9 wherein said catalytic amount of water isabout 0.05 to 0.3 wt. % water, based on the weight of thepolycaprolactam.
 11. A shaped article of manufacture produced byblow-molding the composition of claim
 1. 12. A composition possessingsufficient melt strength for the blow-molding of shaped articlescomprising the reaction product between polycaprolactam, having a meltindex of at least 3 grams/10 minutes, ethylene/vinyl acetate copolymer,gamma-aminopropyltrialkoxysilane and a catalytic amount of water, saidreaction product being substantially free of trialkoxysilane groups,said composition possessing a melt index of below about 2.25 g/10 min.and said ethylene/vinyl acetate copolymer being present in about 5-20weight percent of the composition and said aminosilane compound beingpresent in about 0.01 to 1.0 weight percent of said composition.